The present invention relates to methods and apparatus for leaching constituents from mineral materials and particularly relates to apparatus and methods for distributing leaching solution in a tank containing mineral ores as part of a continuous process for recovering valuable minerals from the ore.
Leaching systems are well known for the recovery of valuable metals from mineral ores. For example, gold or silver has been extracted from ores by leaching the ores with alkaline cyanide solution and oxygen in a continuous, as contrasted with, batch process. The mineral-containing ore is generally crushed and disposed in a slurry through which the leaching solution, i.e., a cyanide solution, is passed. The slurry is leached by using countercurrent leach and wash solutions. The pregnant leaching liquid is usually removed from the top of the tank and passed through a carbon adsorber with the valuable minerals subsequently removed from the loaded carbon material.
In using such systems, it has become increasingly important to minimize their costs. One significant area where costs can be reduced is in the quantity of leaching cyanide, e.g., solution necessary to perform the leaching process. Additionally, in prior systems, the leaching solution enters the lower end of the tank through distribution nozzles in a rotary distribution arm. However, such distribution arms and nozzles are prone to clog and plug. For example, the slurry in the tank may flow into the nozzles and plug them. This may occur upon pump failure or by centrifugal action. As will be recognized, the flow through the nozzles in a conventional distribution arm is provided through a flow conduit common to the nozzles. Thus, when the arm is still rotating, the centrifugal force on the fluid in the arm may cause some leaching fluid to flow out of the end nozzles, only to be replaced by slurry entering the centrally located nozzles. While individual check valves have been proposed in the past, these too will eventually plug. Further, distribution patterns of the leaching solution within the tank using conventional distribution arms have not been wholly satisfactory.
According to the present invention, there is provided apparatus and methods for leaching mineral ores in a continuous process to remove the valuable mineral constituents contained in the ore which reduces the quantity of leaching solution in the slurry exiting the tank and also affords improved control and distribution of the leaching solution within the tank. While the apparatus and methods according to the present invention are particularly applicable to the removal of metals, such as gold and silver, from metal-bearing ores containing such metals, they may also be adaptable to other processes, such as the removal of pyritic, organic and sulfite sulfa compounds present in a solid carbonaceous fuel of the coal or coke type.
According to one aspect of the present invention, there is provided a slurry treatment tank for containing a slurry, preferably mineral-bearing ores, such as gold or sliver ore. Discrete flow paths for the delivery of two treatment solutions into the slurry include a central member rotatable relative to the tank, together with a pair of distribution arms projecting from the central member at different elevations within the tank. Each of those arms has a plurality of outlets or nozzles spaced radially one from the other along their lengths. One of the flow paths conducts a wash solution to the lowermost arm for distribution through its outlets into the lower end of the tank containing the ore slurry. The other flow path conveys leaching solution to each of the outlets in the second distribution arm for distributing leaching solution into the slurry in the tank at an elevation above the lower arm. In this manner, a fraction of the wash solution entering through the lower arm travels upwardly through the ore slurry and carries the leaching solution added to the slurry from the top arm upwardly toward the top of the tank. The slurry exiting the tank at its top therefore contains only a slight amount of the leaching solution, i.e., cyanide, added to the tank through the elevated arm.
According to another aspect of the present invention, there is provided improved control and distribution of the leaching solution in the slurry in the tank. To accomplish this, discrete flow passages or tubes extend through the hub of the distribution arm upwardly into the arm to the respective nozzles or outlets, the latter being spaced radially one from the other along the length of the arm. Each of the discrete conduits includes a flow control valve and a flow meter for controlling the flow of leaching solution through the conduit. Each conduit also carries a check valve. Thus, the flow control valve, in conjunction with the flow meter, controls and indicates the amount of flow to each nozzle. The flow control valves may be adjusted during processing. The check valve maintains the slurry in the tank, preventing it from communicating through the discrete conduits with the source of leaching soution. These flow control devices are connected in each conduit externally of the tank and its hub whereby access for service is provided. By mounting these devices externally, the flows can be monitored and the solution distribution fine-tuned as desired.
Accordingly, it is a primary object of the present invention to provide novel and improved apparatus and methods for minimizing the quantity of the leaching solution exiting the slurry at the top of the tank as well as providing for improved control and distribution of the leaching solution in the slurry in the tank.